The present invention relates to a fuel vapor processing apparatus provided with a canister that is provided with an adsorbent material for adsorbing fuel vapor generated in a fuel tank, and a shutoff valve provided in a vapor passage that connects the canister and the fuel tank.
A related conventional fuel vapor processing apparatus is disclosed in Japanese Laid-Open Patent Publication No. 2011-256778. This fuel vapor processing apparatus is provided with a shutoff valve (control valve) disposed in a vapor passage connecting a canister and a fuel tank. The shutoff valve is provided with a dead band region (valve closing region) cutting off the fuel vapor, and a conducting region (valve opening region) allowing passage of the fuel vapor. In the valve closing state, the fuel tank is maintained in a sealingly closed state, and, in the valve opening state, the fuel vapor of the fuel tank is released to the canister side, making it possible to reduce the internal pressure of the fuel tank. The fuel vapor processing apparatus performs a learning control in which the degree of opening of the shutoff valve is changed at a predetermined speed in the opening direction from the valve closing position, and in which, when the internal pressure of the fuel tank starts to be reduced, the degree of opening of the shutoff valve is stored as the valve opening start position.
However, as compared with the valve opening start time of the shutoff valve, the detection time of the reduction in the internal pressure of the fuel tank is delayed. Therefore, in a learning method in which a stroke amount which is the axial distance of a movable valve portion with respect to a valve seat is gradually changed, it is expected that the shutoff valve is somewhat open from the valve opening start position at the time when the reduction in the internal pressure of the fuel tank is detected. Therefore, there has been a problem that the learning control accuracy for the valve opening start position in the shutoff valve is low.
As a result, there has been a need to improve a learning accuracy for a valve opening start position in a shutoff valve.